Fully-chromophoric ferroelectric nematics for electronic electro-optics

Electronic electro-optic (EEO) phase modulation is a key emerging technology for the chip-scale interconversion of signals between the electronic and photonic domains. The recent discovery of the ferroelectric nematic (NF) liquid crystal phase, a three-dimensional fluid of rod-shaped organic molecules having near-perfect, equilibrium, polar molecular orientational order, offers attractive opportunities for the creation of second-order nonlinear optical materials for EEO. Here we propose and realize a design motif for NF EEO molecules in which few-nanometer-long molecular rods are functionalized both for polarity-dependent electrostatic association, facilitating NF phase formation, and for chromophoric optical nonlinearity, enabling high EEO efficiency, a combination enabling an active second-order nonlinear EEO medium that is 100% chromophoric. We report large EEO coefficients $${r}_{33} \sim 30\ {{\rm{pm}}}/{{\rm{V}}}$$ in two representative NF mixtures (PM618 and PM628) that are comparable to that of the workhorse solid-state electro-optic material lithium niobate. This family of polar fluids offers unique advantages including ease of processing and programmability, with the potential for advanced device modalities. Electronic electro-optic phase modulation enables chip-scale electronic-photonic signal conversion, while ferroelectric nematic liquid crystals provide a promising platform for second-order nonlinear optics. Here, the authors design ferroelectric nematic electro-optic molecules that form a fully chromophoric nonlinear medium with electro-optic coefficients (r₃₃ ≈ 30 pm/V) comparable to lithium niobate.